Current manufacturers of high-speed computer equipment often need to access data information that is communicated on a data bus or other conductors within the equipment for testing or other reasons. Conventional approaches to accessing data on a bus include the use of logic analyzers that provide probes that are placed in electrical contact with the particular conductors in question.
In a typical arrangement, the probes are positioned to obtain the data signals from the target system and the target system is operated to produce the desired data values that are captured by the probes. These data values are acquired and stored in a memory in the logic analyzer. However, many of the target systems that are analyzed using logic analyzers operate at speeds measured in hundreds of megahertz. Consequently, the data values obtained from such a target system will quickly fill up the memory of the logic analyzer. In many cases, this occurs within a few milliseconds.
As a result, logic analyzers have employed circuitry to perform a quick comparison between the values obtained from the target system and desired values specified by the user to detect specific data values from the target system. Generally, only those data values from the target system are stored in the memory of the logic analyzer. In this manner, a reduced number of data values are then stored in the memory of the logic analyzer, thus preventing the memory from becoming full prematurely.
The approaches employed to perform this comparison typically employ logic circuits and other devices of significant size and complexity. Accordingly, such circuits are costly and the number of desired values that may be employed by a single logic analyzer are limited.